'\" et
.TH ERFC "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
erfc,
erfcf,
erfcl
\(em complementary error functions
.SH SYNOPSIS
.LP
.nf
#include <math.h>
.P
double erfc(double \fIx\fP);
float erfcf(float \fIx\fP);
long double erfcl(long double \fIx\fP);
.fi
.SH DESCRIPTION
The functionality described on this reference page is aligned with the
ISO\ C standard. Any conflict between the requirements described here and the
ISO\ C standard is unintentional. This volume of POSIX.1\(hy2017 defers to the ISO\ C standard.
.P
These functions shall compute the complementary error function 1.0 \-
.IR erf ( x ).
.P
An application wishing to check for error situations should set
.IR errno
to zero and call
.IR feclearexcept (FE_ALL_EXCEPT)
before calling these functions. On return, if
.IR errno
is non-zero or \fIfetestexcept\fR(FE_INVALID | FE_DIVBYZERO |
FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.
.SH "RETURN VALUE"
Upon successful completion, these functions shall return the value of
the complementary error function.
.P
If the correct value would cause underflow,
and is not
representable,
a range error may occur, and
\fIerfc\fR(),
\fIerfcf\fR(),
and
\fIerfcl\fR()
shall return
0.0, or
(if the IEC 60559 Floating-Point option is not supported) an
implementation-defined value no greater in magnitude than DBL_MIN,
FLT_MIN, and LDBL_MIN, respectively.
.P
If
.IR x
is NaN, a NaN shall be returned.
.P
If
.IR x
is \(+-0, +1 shall be returned.
.P
If
.IR x
is \-Inf, +2 shall be returned.
.P
If
.IR x
is +Inf, +0 shall be returned.
.P
If the correct value would cause underflow and is representable, a
range error may occur and the correct value shall be returned.
.SH ERRORS
These functions may fail if:
.IP "Range\ Error" 12
The result underflows.
.RS 12 
.P
If the integer expression (\fImath_errhandling\fR & MATH_ERRNO) is
non-zero, then
.IR errno
shall be set to
.BR [ERANGE] .
If the integer expression (\fImath_errhandling\fR & MATH_ERREXCEPT) is
non-zero, then the underflow floating-point exception shall be raised.
.RE
.LP
.IR "The following sections are informative."
.SH EXAMPLES
None.
.SH "APPLICATION USAGE"
The
\fIerfc\fR()
function is provided because of the extreme loss of relative accuracy if
.IR erf ( x )
is called for large
.IR x
and the result subtracted from 1.0.
.P
On error, the expressions (\fImath_errhandling\fR & MATH_ERRNO) and
(\fImath_errhandling\fR & MATH_ERREXCEPT) are independent of each
other, but at least one of them must be non-zero.
.SH RATIONALE
None.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fIerf\fR\^(\|)",
.IR "\fIfeclearexcept\fR\^(\|)",
.IR "\fIfetestexcept\fR\^(\|)",
.IR "\fIisnan\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 4.20" ", " "Treatment of Error Conditions for Mathematical Functions",
.IR "\fB<math.h>\fP"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
